It is known to manufacture articles, or components, using a hot forming process, or a superplastic forming process, in which a hollow metal preform is located in a split hot forming die. The metal preform is heated to a high temperature and pressure is applied internally of the metal preform to form the metal preform into the shape of the split hot forming die.
The split hot forming die is precision cast and precision machined to produce accurately shaped surfaces for the hot forming of the articles or components. The split hot forming die is very expensive to produce and the precision of the surfaces of the split hot forming die determines the shape of the articles or components.
During the hot forming process the high temperature and the pressure applied internally of the metal preform is sufficient to cause the metal preform to become diffusion bonded to the split hot forming die. However, a stop off material, for example boron nitride, is applied to either the surface of the split hot forming die or to the surface of the preform to prevent diffusion bonding between the metal preform and the split hot forming die.
In use the stop off material builds up on the surfaces of the split hot forming die. The stop off material is removed periodically from the surfaces of the split hot forming die because the build up of stop off material gradually effects the quality of the articles, or components, manufactured. Currently the stop off material is removed from the surfaces of the split hot forming die by abrasives, for example grinding wheels, dressing stones etc.
The use of abrasives to remove the stop off material is undesirable because there is a risk that the abrasive may damage the surfaces of the split hot forming die. The damage to the split hot forming die may result in the manufacture of articles, or components, which are not in conformance with the desired shape and size. Additionally the split hot forming die may have to be re-cut to re-produce the accurately formed surfaces of the split hot forming die.